[Reading Science] How Far Has the Dream of the 'Energy Revolution' Artificial Sun Come?

Solar Nuclear Fusion Reproduced on Earth with Ultra-High Temperature and Pressure
Korea's KSTAR Failed to Break Records Last Year Due to Malfunction
Upgraded to Aim for 100 Seconds Operation at 100 Million Celsius by 2025
ITER Fusion Chain Reaction Experiment Success, Targeting Commercialization in 2050s

Can the ‘artificial sun’ truly solve humanity’s energy problems and build a sustainable Earth? Although the United States succeeded in laser-induced ignition (triggering a chain reaction) for the first time late last year, nuclear fusion has yet to take its first proper step toward full-scale energy production. Expectations remain high. If successful, it can provide safe and inexpensive clean energy. This is why seven major countries, including South Korea, are each contributing around 1 trillion won to build the International Thermonuclear Experimental Reactor (ITER) in southern France by 2035, sparking international joint and national research competition.

What is the principle of nuclear fusion energy?

The Sun is a ‘star’ that emits light and heat on its own. Inside the Sun, hydrogen nuclei collide and fuse under gravitational force (nuclear fusion) to form helium, releasing light and heat equivalent to the lost mass in the process. This is ‘nuclear fusion energy.’ It is the exact opposite of conventional nuclear power generation, ‘nuclear fission,’ where heavy atoms like uranium split into lighter atoms upon neutron collision, releasing energy equivalent to the lost mass. Since the 1950s, humanity has been researching how to artificially create such nuclear fusion reactions on Earth to generate energy. On Earth, an ultra-high temperature and ultra-high pressure environment simulating the Sun’s conditions is required because atoms repel each other under normal conditions and never fuse.

The raw materials for nuclear fusion, deuterium, can be extracted from seawater, and tritium can be obtained by bombarding lithium with neutrons inside the fusion reactor. Only some low- to intermediate-level radioactive waste is generated during the power generation process. The reaction can be stopped anytime by simply turning off the plasma generation device, making accidents like those at nuclear power plants highly unlikely. It is considered a safe and inexpensive clean energy source.

Tokamak vs. Laser

To forcibly induce nuclear fusion on Earth, an ultra-high temperature and ultra-high pressure environment is necessary. First, the Tokamak method is being researched. It is the closest to practical application. ITER and KSTAR are examples of the Tokamak method. This method creates a donut-shaped vacuum chamber using powerful superconducting magnets and confines plasma hotter than 100 million degrees Celsius by rotating magnetic fields to sustain the nuclear fusion reaction. Developed in the former Soviet Union in the 1950s, it is the most extensively studied method. The laser method is researched in the United States and parts of Europe. It involves injecting deuterium and tritium into tiny metal spheres and firing ultra-powerful lasers uniformly from all directions. This instantaneously creates ultra-high temperature and pressure inside, forcing hydrogen nuclei to fuse. This is the method by which the Lawrence Livermore National Laboratory in the U.S. announced ignition success (Q>1, meaning more energy produced than input) in December last year. It is the same principle as a hydrogen bomb.

Scientists are cautious about declaring which method is better. Laser fusion proved the theoretical principle of energy production by achieving ignition first. However, the actual energy output relative to input power was absurdly low. It is technically very challenging and costly. On the other hand, the Tokamak method’s technical difficulty is currently achievable with general technology. Although ignition and chain reactions have not yet been achieved, the issue was scale. Once ITER is completed in 2035, it is expected to achieve at least 5 to 10 Q immediately. Yoon Si-won, Deputy Director of the Korea Fusion Energy Research Institute (KFE), said, “For development as an energy source, stability to sustain continuous reactions after a single ignition is most important.”

Meanwhile, KSTAR does not study nuclear fusion chain reactions because neutron shielding is impossible. It is used for applied technology research, such as maintaining plasma at 100 million degrees Celsius. ITER is equipped with neutron shielding devices and can conduct full-scale research on blanket technology for nuclear fusion chain reactions and energy production.

The mystery of 100 million degrees Celsius

The 100 million degrees Celsius at which nuclear fusion occurs is an unimaginable temperature. How is it created and managed? Think of a microwave oven. First, the inside of the Tokamak is made a vacuum, then superconducting magnets are activated to form a donut-shaped magnetic field. Deuterium and tritium are injected, and an electric field is generated. The injected gases collide with accelerated electrons, forming plasma. This is the same principle as heating food with microwaves. KSTAR uses two heating devices capable of generating 6 MW-class electromagnetic waves. It also uses superconducting magnets to eliminate heat generation. This was the secret behind South Korea’s record of maintaining plasma hotter than 100 million degrees Celsius for over 30 seconds since KSTAR’s operation began in 2008 and achieved in 2021. Many wonder how the fusion reactor can withstand such a temperature. The ultra-hot plasma is levitated by magnetic fields, so it does not directly affect the reactor’s surface. Still, since the internal temperature exceeds thousands of degrees, a heat-resistant device called a divertor is installed. Temperature measurement is done by analyzing the plasma’s color.

Why did last year’s record attempt fail?

South Korea has set world records for maintaining ultra-hot plasma every year since 2018, surpassing 30 seconds in 2021. Experts believe that achieving 300 seconds would enable mastering the operation and management technology of the ‘artificial sun.’ Although 50 seconds was initially expected last year, no news came. It turned out that heating equipment malfunctioned, leading to a three-month repair period. On the 22nd of last month, KFE disclosed this to the press and announced improvements allowing repairs within one week if malfunctions occur in the future. They also pledged to strive for 50 seconds this year and 100 seconds by 2025.

Tungsten divertor sample developed for KSTAR upgrade. Photo by KFE.

The revamped KSTAR

To this end, KFE recently upgraded the carbon material divertor (heat-resistant material) to tungsten. Tungsten has the highest melting point among existing materials at 3,422 degrees Celsius, expected to greatly improve the reactor’s lifespan and performance. Additionally, a 6 MW-class electromagnetic wave generator that shoots particle beams inside the reactor will be installed. Alongside this, a virtual fusion reactor and simulator were created using a supercomputer purchased for 7.5 billion won. This facility displays real-time anomalies inside the reactor during operation and allows virtual operation for pre-experiment practice. A KFE official explained, “We developed the supercomputer program using our own personnel,” adding, “It will greatly aid research and development to stably expand the scale of experiments in the future.”